1. Field of the Invention
The present invention relates to an electronic air-fuel mixture control system for internal combustion engines, more particularly to an electronic air-fuel mixture control system for determining an optimum air-fuel ratio in dependence upon learning values renewed in response to change of the load acting on the engine.
2. Discussion of the background
Such an electronic air-fuel mixture control system as described above has been proposed in the Japanese Patent Early Publication No. 58-150057, wherein a plurality of learning values related to a plurality of load regions are selectively renewed in response to change of the load acting on the engine so as to determine an optimum air-fuel ratio in dependence upon the renewed learning value. In such selective learning of the learning values, it is, however, observed that the learning values are only partially renewed when the engine load is frequently detected in a limited load region. For this reason, it is unable to quickly conduct uniform learning of the plural learning values in response to change of the engine load. This results in difficulty in reliable determination of the optimum air-fuel ratio for various operations of the engine.